exception during macro expansion: [error] java.lang.IllegalStateException: Invalid group by aggregation:

Question

I have a table like this in MYSQL.

create table Employee(
 id tinyint,
 name char(36),
 is_permanent tinyint,
 company_name char(36),
 designation Char(36),
 primary key (id)

);

and I want to write a SELECT query on this table with Quill SQL.

 select count(1),  sum((case when (`designation` = 'software') then 1 else 0 end)) from employee group by company_name;

I wrote a model and

case class Employee(id: Int,
                    name: String,
                    is_permanent: Boolean,
                    company_name: String,
                    designation: Designation)

  trait Designation {
   val value: String
  }

  case object SoftwareEngineer extends Designation {
     override val value: String = "software"
  }

 case object MechanicalEngineer extends Designation {
   override val value: String = "mechanical"
  }

My query using quill is

ctx.run {
  query[Employee].groupBy(_.company_name).map {
    case (compName, employeeTable) =>
      (employeeTable.size,
       employeeTable.filter(_.designation == lift(SoftwareEngineer)).size,
       compName)
  }
}

where ctx is the quill context.

However the compiler shows an error that

exception during macro expansion: 
 [error] java.lang.IllegalStateException: Invalid group by aggregation: 'x48.filter(x49 => 
 x49.designation == ?).size'

Is the way of calculating filtered count in the group by clause correct ? If no, Is there other way to do it ?

Answer 1

The way to find out conditional count for a group by clause is NOT

 employeeTable.filter(_.designation == lift(SoftwareEngineer)).size,

but

 employeeTable.map { i =>
          if (i.`designation` == lift(SoftwareEngineer)) 1
          else 0
        }.sum

Of course with proper encoder defined for designation